How to: film canister rocket launch

8 Mar

Put this into the category of ‘fun things to do in the kitchen’ (while wearing proper eye protection).

The yard might be a better place for this one though, so you don’t put any film canister dents into your ceiling. When it takes off, it does have quite a pop (but equally it is pretty light).

What you need:

– 1/2 an Alka Seltzer tablet (aka sodium bicarbonate)
– 1 film canister
– 15mL of water
– wear eye protection

What you do:

– Put 15mL of water into the film canister (fill it about 1/2 way)
– Drop in the 1/2 Alka Seltzer into the water
– Put the lid on tight and give it a quick shake
– Put the canister down, upside down

Within a few seconds, the Alka Seltzer will partially dissolve. As it does this, it will give off some CO2 gas. As the pressure mounts, the film canister will get to a point where the lid can no longer contain the amount of gas inside.

When this happens, the lid pops off to release the pressure.



Thanks to Mr. Newton, we understand that when the pressure is released in a downward direction, the equal and opposite force reaction occurs, propelling the film canister up.

And in this particular example, I calculated the launch speed is 5.8m/s.

How I calculated this: the GoPro was shooting at 60fps, so each frame = 0.017 seconds. Looking at the footage, the canister moved about 10cm in a single frame. Using V=d/t, moving 10cm in 0.017s works out to 588cm/s or 5.8m/s.

Simple as that.

Modifications to try:

– Change the ratio of Alka Seltzer and water.
– Use vinegar & baking soda instead of sodium bicarbonate & water.
– If your camera doesn’t shoot at 60fps, just divide 1 by however many frames it shoots per second (e.g. if it films at 24fps, each frame is 0.04 seconds: 1/24=0.04).

Of course this little rocket doesn’t entirely do justice to how real rockets launch, in terms of fuel, ignition process, etc. – but it does provide a great little demo of Newton’s third law (with a little of the second law mixed in for good measure).

Jesse and I did this one on TV last week in the second half of our weekly Beyond The Sun space segment on Sun News Network, talking about a couple real-life rocket launches:

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